Gas turbine plant



March 24, 1953 w. MacT. oGsToN 2,632,297

@A s TURBINE PLANT Filed Aug. 12,@949

Attorneys hot gas under pressure. invention is concerned with the casewhere work- Patented Mar. 24, 1953 GAS TURBN E PLANT Walter MacTavishOgston, Dumfries, Scotland,

assigner to Power Jets (Research and Development) Limited, London,England, a British Company Application August 12, 1949, Serial No.109,841

In Great Britain August 27, 1948 1 claim. l

This invention relates to improvements in gas turbine plant when appliedto the generation of More particularly the ing fluid exhausted from agas turbine imparts heat indirectly through a heat exchanger to apressurised gas stream, such an arrangement being adopted, for example,when it is desired to generate a hot high pressure stream of air orother gas with its oxygen content conserved and which cannot thereforebe heated by having fuel burnt in it. The invention is envisaged ashaving particular application to the formation of a hot air blast forblast furnace operation but may be also applied wherever a stream of hotcompressed gas is required.

As is known, the usual method of heating air for use as an air blast ina blast furnace is to burn a portion of the blast furnace exhaust gasand to pass the hot products of combustion produced thereby for a givenperiod through one of two regenerative heat exchangers of the Cowperstove or chequer brick type, after which the supply of hot gas istransferred to the other stove while cold air is passed through the hotstove to lbe heated on its Way to the blast furnace. The flows of hotgas and cold air are reversed after a certain period and thesealterations are continually repeated.

One disadvantage of such an arrangement is that due to the substantialpressure of the cold air above atmospheric there is a considerable lossin heat when the two gas ows are reversed. A

, further disadvantage is that the above-mentioned stoves arenecessarily very large and consequently very costly.

One object of the present invention is toavoid these disadvantages andaccordingly the invention provides a generator of hot high pressure gascomprising means for supplying pressurised gas, a continuously operableheat exchanger for receiving and indirectly heating said pressurised gassupply, means for supplying hot gas to said heat exchanger to effectsuch heating comprising a multi-stage gas turbine from which the hot gassupply is derived at an intermediate pressure stage, which stage is soselected that the hot gas pressure is similar to that of the gas to beheated thereby.

The heat exchanger is preferably of the regenerative kind and comprisesa rotary disc or drum containing a matrix having a large number of smallaxial or radial channels respectively through which the two gas streamsow in opposite directions. It is well known that heat exchangers of thistype have in general, important advantages in respect to bulk andefficiency compared with heat exchangers of other kinds, but have theattendent disadvantage that effective sealing against leakage betweenthe respective gas streams is difficult tol achieve and maintain;however, the difficulty is minimised when the gas streams are at similarpressures, and it is this condition which the invention is intended tobring about. In a preferred form of the invention intended particularlyfor use in blast furnace operation, the gas to be indirectly heated isair which is compressed in a compressor driven by the turbine rotor.Preferably this compressor is a multi-stage one from which the air to beheated is taken oi at an intermediate stage, while air for the turbineworking fluid is taken off at the final stage. The latter, in theparticular application to blast furnaces, is burnt with blast furnaceexhaust gas as the fuel, which is first raised to an appropriatepressure by a gas compressor mounted on the same shaft as the maincompressor.

Preferably the hot gas stream is derived from the outlet of one highpressure stage turbine coupled to a second low pressure stage turbineand both driving the compressor. The hot gas from the outlet of the highpressure turbine may be burnt with additional fuel before it passesthrough the heat exchanger and this fuel may also be blast furnace gasderived from an intermediate stage of a multi-stage gas compressor.

After passing through the heat exchanger, the gases pass through thesecond or low pressure turbine from the outlet of which they passdirectly to atmosphere or through an auxiliary I heat exchanger, whichmay be of the tubular recuperative type, for heat exchange with air tobe used as blast air and derived from an intermediate stage of the aircompressor.

By way of example one embodiment of the preferred form of the inventionis now described in detail with reference to the accompanying drawingwhich represents schematically the plant arrangement of a hot highpressure gas generator for supplying blast air to a furnace. The plantincludes a low pressure compressor stage I, a high pressure compressorstage 2, a high pressure turbine stage 3 and a low pressure turbinestage 4 all mounted on the same shafting so that the two turbine stagerotors drive the two compressor stages.

Air from the atmosphere enters the low pressure compressor stage I and,when discharged therefrom is divided, a proportion of the air beingtaken through an auxiliary heat exchanger for heat exchange with hotexhaust gases leaving the low pressure turbine stage 4, and subsequentlyto a main rotary regenerative heat exchanger 6 from which the air, beingboth pressurised and heated, passes to the tuyres lof a blast furnace 1.The remainder of the lair discharged from the low pressure compressorstage I passes to the high pressure compressor stage 2 and thence to acombustion chamber 8 where it supports the combustion of a fuel; thecombustion products pass to the high pressure turbine stage 3 and thento a reheat combustion chamber 9 where more fuel is burnt, beforepassing successively through 'the main heat exchanger 6, the lowpressure turbine stage 4 and the auxiliary heat exchanger 5, and finallyexhausting to atmosphere.

Fuel economy in the plant is eifected lby utilising a portion of theblast furnace exhaust gases as fuel for heating purposes. Thus, thesegases are collected at the furnace upstakes IB and, after suitablycleaning and cooling, are led to a two-#stage gas 4compressor I I, I 2which -is driven by the main turbo-compressor rotor; after compressionin the low pressure stage I I a proportion o'f the fuel gas is bled offand delivered to the reheat c'zoinbustion chamber 9., While theremainder is -fully' "cmpressed in the high pressure stage I2 cf the gas`compressor and is delivered to the combustion chamber 8.

An 'electric power 4ge'rierator I3 is also driven from theturbo=cornpressor shaft and provides an outlet for surplus powerproduced in the plant; provision may also be made for motoring thisgenerator in order t'o start the plant, using power previouslyaccumulated.

If the plant is arranged for normal operation on a constant pressurecycle, that for combustion in each -of the `combustion chambers 9 and 9to take place without a substantial variation Vin gasrpressures, it is`apparent that by selecting similar pressure ranges for the highpressure compressor and turbine stages 2 and 3- respectively, 'a low ornegligible pressure differential in the heat exchanger 6 is ensured.Furthermore, the lhigh pressure stage I2 `of the fuel gas Vcom-Apre'ssor'ma'y be similarly selected so that both the lfuel and 'thecombustion-supporting gases are supplied at similar pressures to each ofthe respective combustion chambers.

Although the invention is of particular advantage for use with a rotaryregenerative heat exchanger, due to the elimination of the necessity forpressure resistant gas seals and "so making .possible high rotary speed,it also presents advantages when used in combination with 'a recu-.fperative heat exchanger, for example, of the tu- 4 bular type since,due to the pressure of the air and gas ows being approximately equal,the walls of the tubes may be relatively thin and will therefore be lesscostly and lighter.

I claim: Y Gas turbine power plant for supplying -a blast ,of hot airunder pressure suitable for use in a blast furnace, including a lowpressure compressor stage supplying at an intermediate pressure bothblast and other air, a high pressure compressor stage receiving saidother air from said low pressure compressor stage and delivering it at ahigher pressure, a high pressure turbine stage and a low pressureturbine stage driving said high and low pressure compressor stages, acombustion chamber receiving said other air from said high pressurecompressor stage and supplying combustion products to said high pressureturbine stage, and a heat exchanger, of the type having a continuouslymoving element transferring heat between independent gas streams,receiving on the one Ahand blast air from said 10W pressure compressorstage to be heated and on the other hand combustion products from saidhigh pressure turbine stage to heat the blast air, said combustionproducts being delivered thereafter to-,said low pressure turbine stage,the intervmediate pressure yof the combustion products during heatexchange being not greatly different from that of the blast air so thatleakage between 'their independent stream in the heat exchanger tends tobe minimized.

WALTER MACTAVISH OGSTON.

REFERENCES CITED i The following references are of record in the le ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Ser. No. 217,505, Jendrassik (A.l?. 0.), published April 27, 1943.

